I use a 7mm mag 139g - 165g depends on the wind. Its usually long range running shots. They are very curious animals and you may coax them in even by wavying a white cloth. Some desparate hunters will run them up to a fence, then take there shot, as Antelope do not jump fences, at least not very sucessfuly. A 243 will work ok at the low end. If you are glassing them with 7x they can see you as good or better, and they rely on there speed as there defence. Hope this helps.
Jim